<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<script>
			var num;
			console.log(num);//undefined\
			num = null;
			console.log(num);
			console.log(typeof(num));
			
			num = 3.14;
			console.log(num);
			console.log(typeof(num));
			
			num = "hello js";
			console.log(num);//hello js
			console.log(typeof(num));
			
			// 全等 ===
			// 不全等 !==
			var m = "3";
			var n = 3;//number
			if( m == n ) { //只是比较值是否相等
				console.log("m == n");
			}
			if( m === n ){ //不仅比较值,也比较了数据的类型
				console.log(m === n);
			}else{
				console.log(m !== n);
			}
			
			
		</script>
		
	</body>
</html>
